German Published, Non-Examined Patent Application DE-OS No. 37 04 56 discloses a production process for such polymer film filters in which a film having a support structure is produced by plastic injection molding in an injection mold; the film is then masked suitably and acted upon with penetrating irradiation only on the thin film regions which are not intended to function as the support walls, and the beam tracks of the irradiation are then widened into micropores by means of a solvent. This process is suitable only for producing filters of this kind individually, because an injection mold for producing a structure of film thickness must be produced and operated with very high accuracy and close tolerances, and this limits its size. The subsequent steps can also be carried out only with complicated, labor-intensive individual filter manipulation. This results in a very expensive product.
U.S. Pat. No. 3,852,134 discloses a process for producing polymer film filters in a continuous operation, the filters having continuous pores only in predetermined regions. These filters are produced in such a way that the dense film is exposed to particle irradiation the tracks of which cause etchable structural faults. These tracks are sensitized in the predetermined regions by irradiation with ultraviolet light, after which a first pre etching is done until the sensitized tracks are etched through with narrow pores, but wherein the unsensitized tracks penetrate the film only partly. After that, a heat treatment that repairs the remaining tracks is performed, after which the narrow pores are widened in a further etching step. In this way, the non-porous regions are covered with blind bores. This five-step process, with five passages of the films, is quite complicated and labor. intensive.
U.S. Pat. No. 3,438,50 also discloses the production of polymer filters, which have continuous pores only in predetermined regions, in a continuous operation by irradiating the film through an irradiation-impermeable mask with particle irradiation that produces tracks, after which the etching of the tracks to make pores is performed. The disadvantage here is that the mask must already be furnished for the film irradiation, which is done in a vacuum and is expensive, and must be introduced into the vacuum chamber and there moved along with the film, and a later predetermination of the porous regions is not possible. The mask which moves along with the film makes it more difficult to introduce very fine masking patterns.